The field of the invention relates to phyllosilicate minerals such as, for example, the serpentines and micas, which exhibit in their structure, sequentially, octahedral layers containing oxides of magnesium, aluminum and/or iron, and tetrahedral layers of silicon and oxygen, which minerals have been modified for the purpose of rendering them oleophilic or imparting to them certain other desirable properties through having been coated by organo-silanes. The invention further relates to a method for conditioning said minerals to enable same to react on their surfaces with organo-silanes and to methods for effecting coatings on said minerals with organo-silanes. Minerals treated in accordance with the invention retain their basic structural integrity as evidenced by the fact that they exhibit the same X-ray diffraction pattern as do untreated minerals.
In the past, it has been recognized that certain phyllosilicate minerals possess desirable characteristics for use in plastics and elastomer compounding. In such applications, the most important active functions of these materials are reinforcement, improvement of mechanical properties, heat resistance and flow control. In addition to the above uses, certain of these minerals have found applications as additives in oil-based fluid systems, such as, for example, lubricants, paints and oil well drilling fluids for modification to flow properties. But in such applications, the unmodified minerals suffer the innate limitation of being wet by water in preference to oil so that composites incorporating them generally show impaired performance in the presence of moisture. Further, the unmodified minerals do not ordinarily interact positively with oils, plastics and elastomers forming at best only simple dispersions therein upon physical mixing without any significant chemical bond being formed between the minerals and the continuous phase. Such dispersions are usually metastable with the minerals tending to segregate from the continuous phase. It has now been discovered that by superficially coating the preconditioned surface of these minerals through chemical reaction with organo-silanes the above-noted deficiencies can be overcome.
A technique of reacting said minerals with organo-silanes has been reported in the prior art. See French Pat. No. 2,098,467 issued Feb. 14, 1972. In this prior art, the layered minerals which are made up of alternating sheets of magnesia and silica are subjected to the simultaneous action of organo-silanes in concentrated mineral acid solution. The effect of this solution on the layered mineral is to replace the magnesia layer with the organo-silanes, the process continuing throughout the entire layered mineral system. The procedure results in the elimination of most, if not all, of the magnesia layers leaving the alternating silica layers separated by layers of chemically reacted organo-silane. The reaction is an in-depth reaction controlled by the rate of diffusion of the acid and organo-silane into the body of the mineral as evidenced by the required use of a large excess of concentrated acid, long reaction periods and elevated temperatures.
The overall result of these combined reactions is that instead of a superficial acid etch, i.e., removal of the outer octahedral magnesium layer followed by surface reaction of the exposed surface silanol groups with the organo-silane, the reaction described in the prior art proceeds in depth removing most of the total magnesia (or isomorphically substituted metal) leaving an amorphous silica residue. This silica pseudomorph, which lacks crystalline structure, is friable and has, of itself, little or no mechanical strength. According to the prior art, this material is a distinct organo-mineral polymer in contrast with the superficially coated crystalline minerals of the present invention. Even in cases where only a relatively small amount of magnesia is eliminated using the prior art method organo-mineral polymer is still formed as shown by significant alteration of the X-ray diffraction pattern of the original mineral, specifically a low angle X-ray diffraction peak appears signifying the presence of alternating organo-silane-silicon layers.